Training hones the ear of the budding musician, refines the palate of the candidate sommelier, and sharpens the eye of the student artist. This ability to improve our perceptual skills- to get better with practice- is critical for the acquisition of many complex behaviors, including speech and language. The fundamental importance of perceptual learning, and the promise it holds for enhancing communication abilities, makes it of vital interest to determine how training-based improvements are implemented in the brain. By measuring and manipulating the activation of neural circuits in freely-moving, behaving animals, the Caras Lab seeks to understand how sensory and cognitive systems work together to enable perceptual learning.

Role of frontal cortex in perceptual learning

Our recent work (Caras and Sanes, 2017) suggests that the top-down networks that modulate auditory cortical activity are strengthened during perceptual training. Multiple lines of evidence implicate frontal cortex as a key node in this process. To explore this possibility, we are using a wireless recording approach to monitor frontal cortical activity in freely-moving Mongolian gerbils as they train and improve on sound detection and discrimination tasks. In addition, we plan to employ a fully-integrated, custom-designed telemetric recording and optogenetic system to simultaneously measure and manipulate activity in a cell-type specific and temporally precise manner.

Neural pathways supporting auditory cortical modulation

Multiple neural circuits are likely to contribute to auditory cortical plasticity during perceptual learning. We are using a combination of fluorescent dyes, viral vectors, and immunohistochemistry to establish the anatomical inputs to gerbil auditory cortex, with the goal of identifying layer and cell-type specific targets. Future experiments will use both optogenetic and chemogenetic approaches to assess and manipulate functional connectivity.

Neuromodulatory mechanisms of perceptual learning

A substantial body of literature indicates that neuromodulators, such as acetylcholine, noradrenaline, and dopamine, are involved in associative learning and cortical plasticity. While many of these same neuromodulatory systems are also likely to play an active role in perceptual learning, many details remain uncertain, including the specific neuromodulators involved, their sites of action, and how different modulatory systems work synergistically to enable training-based improvements in cortical and perceptual sensitivity. To address these issues, we are using targeted pharmacological manipulations to determine whether the activation or blockade of specific receptor subtypes facilitates or attenuates perceptual improvement.